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| United States Patent |
5,719,212
|
|
Nakae
, et al.
|
February 17, 1998
|
Powder coating composition of epoxy-containing acrylic, polycarboxylic
acid and antioxidant
Abstract
Disclosed is an acid-epoxy curing type powder coating composition which
forms a coated film having excellent yellow resistance and appearance. The
powder coating composition comprises:
(A) an epoxy group-containing acrylic resin prepared by polymerizing the
monomer mixture which comprises,
(a) 35 to 65% by weight of an epoxy group-containing ethylenically
unsaturated monomer, and
(b) remainder amount of an ethylenically unsaturated monomer which is
different from the epoxy group-containing ethylenically unsaturated
monomer;
(B) a polycarboxylic acid; and
(C) an antioxidant having a melting point of from 50.degree. to 140.degree.
C.
| Inventors:
|
Nakae; Yasuhiko (Kyoto, JP);
Nakatsuka; Hitoshi (Neyagawa, JP);
Inoue; Koichi (Amagasaki, JP)
|
| Assignee:
|
Nippon Paint Co., Ltd. (Osaka, JP)
|
| Appl. No.:
|
740349 |
| Filed:
|
November 8, 1996 |
Foreign Application Priority Data
| Current U.S. Class: |
523/451; 523/453; 523/455; 523/456 |
| Intern'l Class: |
C08K 063/00 |
| Field of Search: |
523/451,453,455,456
|
References Cited
U.S. Patent Documents
| 5034432 | Jul., 1991 | Ueno et al. | 523/221.
|
| 5266652 | Nov., 1993 | Toyoda et al. | 525/386.
|
| 5270391 | Dec., 1993 | Miyazaki et al. | 525/194.
|
| 5468813 | Nov., 1995 | Uenaka et al. | 525/386.
|
| Foreign Patent Documents |
| 55-140060 | Nov., 1980 | JP.
| |
| 56-20072 | Feb., 1981 | JP.
| |
| 63-165463 | Jul., 1988 | JP.
| |
| 4-332748 | Nov., 1992 | JP.
| |
Primary Examiner: Sellers; Robert E.
Attorney, Agent or Firm: Townsend&Banta
Claims
What is claimed is:
1. A powder coating composition comprising:
(A) an epoxy group-containing acrylic resin prepared by polymerizing a
monomer mixture which comprises,
(a) 35 to 65% by weight of an epoxy group-containing ethylenically
unsaturated monomer, and
(b) remainder amount of an ethylenically unsaturated monomer which is
different from the epoxy group-containing ethylenically unsaturated
monomer;
(B) a polycarboxylic acid; and
(C) from 0.1 to 10 parts by weight based on 100 parts of the total weight
of epoxy group-containing acrylic resin (A) and polycarboxylic acid (B) of
an antioxidant having a melting point of from 50.degree. to 140.degree. C.
2. The powder coating composition according to claim 1, wherein the molar
ratio of an epoxy group contained in the epoxy group-containing acrylic
resin (A) to a carboxyl group contained in the polycarboxylic acid (B) is
10/10 to 10/5.
3. The powder coating composition according to claim 1, wherein the
antioxidant (C) comprises a phosphite antioxidant.
4. The powder coating composition according to claim 1, wherein the
antioxidant (C) comprises a combination of a phenol antioxidant and a
phosphite antioxidant.
5. The powder coating composition according to claim 3, wherein the
phosphite antioxidant is represented by the formula:
##STR2##
wherein, R.sub.1 represents a hydrogen atom, a t-butyl group, or a phenyl
group, R.sub.2 represents a hydrogen atom, a methyl group, a t-butyl
group, or a phenyl group, and R.sub.3 represents a hydrogen atom, or a
methyl group.
6. The powder coating composition according to claim 1, wherein the monomer
mixture comprises 40 to 62% by weight of the epoxy group-containing
ethylenically unsaturated monomer (a).
7. The powder coating composition according to claim 1, wherein the epoxy
group-containing acrylic resin (A) has a SP value of from 11.0 to 11.6.
8. The powder coating composition according to claim 1, wherein the epoxy
group-containing acrylic resin (A) has a glass transition temperature of
not less than 20.degree. C.
9. The powder coating composition according to claim 1, wherein the monomer
mixture comprises 0.1 to 10% by weight of isobutyl methacrylate as the
ethylenically unsaturated monomer (b) which is different from the epoxy
group-containing ethylenically unsaturated monomer (a).
10. The powder coating composition according to claim 1, wherein the
polycarboxylic acid is decanedicarboxylic acid.
11. The powder coating composition according to claim 1, wherein coating
particles of the powder coating composition have a mean particle size of
not more than 15 micron.
12. A clear powder coating composition comprising the powder coating
composition according to claim 1 as a binder component.
13. The powder coating composition according to claim 4, wherein the
phosphite antioxidant is represented by the formula:
##STR3##
wherein, R.sub.1 represents a hydrogen atom, a t-butyl group, or a phenyl
group, R.sub.2 represents a hydrogen atom, a methyl group, a t-butyl
group, or a phenyl group, and R.sub.3 represents a hydrogen atom, or a
methyl group.
Description
FIELD OF THE INVENTION
The present invention relates to a curable resin composition which is
suitable for an automotive top coating composition and a coil coating
composition.
BACKGROUND OF THE INVENTION
In recent years, it is generally desired to have a coating composition
which releases a decreased amount of solvent in the air. Therefore, powder
coating compositions are attracting notice in the art.
On the other hand, there has recently been the problem that of coated films
being damaged by acid rain, and a coated film having good acid resistance
is desired. The coated film obtained by a curing system of acid-epoxy
type, generally has good acid resistance.
However, a coating of an acid-epoxy type readily colors when it is cured by
baking. Thus, a curing system of acid-epoxy type is difficult to be
applied on pail colors, such as white and mica.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an powder coating
composition of acid-epoxy curing type which forms a coated film having
excellent yellow resistance and appearance, and a method for forming a
coated film using the same.
That is, the present invention provides a powder coating composition
comprising:
(A) an epoxy group-containing acrylic resin prepared by polymerizing the
monomer mixture which comprises,
(a) 35 to 65% by weight of an epoxy group-containing ethylenically
unsaturated monomer, and
(b) remainder amount of an ethylenically unsaturated monomer which is
different from the epoxy group-containing ethylenically unsaturated
monomer;
(B) a polycarboxylic acid; and
(C) an antioxidant having a melting point of from 50.degree. to 140.degree.
C.
DETAILED DESCRIPTION OF THE INVENTION
Epoxy group-containing acrylic resin (A)
The epoxy group-containing acrylic resin (A) employed in the present
invention is prepared by polymerizing the monomer mixture which comprises
an epoxy group-containing ethylenically unsaturated monomer (a), and an
ethylenically unsaturated monomer (b) which is different from the epoxy
group-containing ethylenically unsaturated monomer (a).
The wording "monomer" means "ethylenically unsaturated monomer"
hereinafter.
The epoxy group-containing monomer (a) is the compound which has an epoxy
group, and a copolymerizable double bond. The monomer (a) has relatively
low molecular weight, that is, it has generally not more than 10,
preferably not more than 8 carbon atoms.
Examples of the monomer (a) include glycidyl acrylate, glycidyl
methacrylate, .alpha.-methyl glycidyl acrylate, and .alpha.-methyl
glycidyl methacrylate. Two or more of these monomers may be used in
combination.
The monomer (b) which is different from the epoxy group-containing monomer
(a), is the compound which has a copolymerizable double bond, and is
compatible with an epoxy group. The monomer (b) also has relatively low
molecular weight.
Examples of the monomer (b) include alkyl esters of (meth)acrylic acid such
as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate,
isobutyl (meth)acrylate t-butyl (meth)acrylate 2-ethylhexyl
(meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl
(meth)acrylate, and cyclohexyl (meth)acrylate; hydroxyalkyl esters of
(meth)acrylic acid such as hydroxyethyl (meth)acrylate, and hydroxypropyl
(meth)acrylate; styrene; vinyl toluene; .alpha.-methylstyrene;
acrylonitrile; methacrylonitrile; acrylamide; dimethylacrylamide; and
dialkyl esters of unsaturated dibasic acid. Two or more of these monomers
may be used in combination.
The monomer (a) is contained in the monomer mixture in an amount of from 35
to 65% by weight, preferably 40 to 60% by weight, more preferably 45 to
60% by weight based on the total amount of the monomer mixture. If the
content of the monomer (a) is less than 35% by weight, curability of the
resulting coating composition may become poor. If the content is more than
65% by weight, clearness of the resulting coated film may become poor and
the appearance thereof may become defective.
It is preferred that the monomer mixture contains 0.1 to 10% by weight of
isobutyl methacrylate as the monomer (b). This is because the blocking
resistance of the resulting powder coating composition is improved.
The monomer mixture is polymerized according to any of the conventional
procedures well known to those skilled in the art, to prepare the epoxy
group-containing acrylic resin (acrylic polyepoxide) (A).
The resulting epoxy group-containing acrylic resin (A) has a solubility
parameter of generally 11.0 to 11.6, preferably 11.0 to 11.4. The powder
coating composition may have improved curability at low temperature, and
the coated film may have improved clearness, by employing such an epoxy
group-containing acrylic resin (A). The solubility parameter (It is
referred to as "SP value" hereinafter.) may be measured according to the
turbid point titration method described in Suh & Clarke, J. Polymn. Sci.,
A-1, 5, pages 1671-1681, 1967. For example, the method may be carried out
using a tetrahydrofuran (THF) solvent at a measuring temperature of
20.degree. C.
The epoxy group-containing acrylic resin (A) has a glass transition
temperature of preferably 20.degree. to 60.degree. C., more preferably
35.degree. to 58.degree. C. If the glass transition temperature is less
than 20.degree. C., blocking resistance of the resulting powder coating
composition may become poor. If the glass transition temperature is more
than 60.degree. C., appearance of the resulting coated film may become
defective.
Polycarboxylic acid (B)
The polycarboxylic acid (B) employed in the present invention is the
compound which has not less than 2 carboxyl groups. This is the component
which cures a coating of the powder coating composition. The
polycarboxylic acid (B) reacts with epoxy groups contained in the epoxy
group-containing acrylic resin (A). Thereby, the epoxy group-containing
acrylic resin (A) is crosslinked.
Examples of the polycarboxylic acid (B) include aliphatic dibasic acids
such as adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid,
hexadecanedicarboxylic acid, eicosanedicarboxylic acid, and
tetraeicosanedicarboxylic acid; aromatic polycarboxylic acids such as
isophthalic acid, and trimellitic acid; and alicyclic dibasic acids such
as hexahydrophthalic acid, and tetrahydrophthalic acid. Preferred
polycarboxylic acid (B) among them is decanedicarboxylic acid.
Antioxidant (C)
The antioxidant (C) employed in the present invention is not particularly
limited, and may be any which is employed conventionally by those skilled
in the art. Preferred antioxidant (C) has a melting point of generally
50.degree. to 140.degree. C., preferably 75.degree. to 125.degree. C. If
the melting point of the antioxidant (C) is less than 50.degree. C.,
blocking resistance of the resulting coated film becomes poor, and if it
is more than 140.degree. C., the antioxidant becomes difficult to melt at
a usual baking temperature, the agglomerates thereof are left on the
coated surface, and appearance of the coated film may become defective.
The antioxidant (C) is preferably at least one selected from the group
consisting of a phenol antioxidant, a phosphite antioxidant and a
thioether antioxidant. Particularly preferred is the phosphite
antioxidant.
The antioxidants of each class may be used alone, but it is preferred that
two or more classes of these antioxidants are used in combination in order
to prohibit the yellowing of the polymer, because the mechanism for
prohibiting the oxidation is different depending on the class of
antioxidant used. Preferred is a combination of the phenol antioxidant and
the phosphite antioxidant, or a combination of the phenol antioxidant and
the thioether antioxidant. Particularly preferred combination for
improving the yellow resistance is a combination of the phenol antioxidant
and the phosphite antioxidant.
Examples of the phenol antioxidant include those commercially available as
Sumilizer BHT, Sumilizer S, Sumilizer BP-76, Sumilizer MDP-S, Sumilizer
BP-101, Sumilizer GA-80, Sumilizer BBM-S, Sumilizer WX-R, Sumilizer NW,
Sumilizer GM, Sumilizer GS, and Sumizal BHT
(2,6-di-t-butyl-4-methylphenol) from Sumitomo Kagaku K.K.; as Adekastab
AO-20, Adekastab AO-30, Adekastab AO-40, Adekastab AO-50
(n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), Adekastab
AO-60 (tetrakis-{methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate}me
thane), Adekastab AO-75, Adekastab AO-80
(3,9-bis-›2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimet
hylethyl!-2,4,8,10-tetraoxaspiro{5,5}undecane), Adekastab AO-330, Adekastab
AO-616, Adekastab AO-635, Adekastab AO-658, Adekastab AO-15, Adekastab
AO-18, Adekastab 328, Adekastab AO-37 from Asahi Denka K.K.; as Sanol LS
2626
(1-›2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}ethyl!-4-{3-(3,5-di-
t-butyl-4-hydroxyphenyl)propionyloxy}-2,2,6,6-tetramethylpiperidine) from
Sankyo K.K.; and the like.
Preferred phenol antioxidants are 2,6-di-t-butyl-4-methylphenol having a
melting point of 71.degree. C.,
n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate having a melting
point of 50.degree. C.
tetrakis-{methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate}methane
having a melting point of 115.degree. C.,
3,9-bis-›2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimeth
ylethyl!-2,4,8,10-tetraoxaspiro{5,5}undecane having a melting point of
125.degree. C., and
1-›2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}ethyl!-4-{3-(3,5-di-t
-butyl-4-hydroxyphenyl)propionyloxy}-2,2,6,6-tetramethylpiperidine having a
melting point of 135.degree. C.
Examples of the phosphite antioxidant include those commercially available
as Sumilizer TNP, Sumilizer TPP-R, Sumilizer P-16 from Sumitomo Kagaku
K.K.; and as Adekastab PEP-2, Adekastab PEP-4C, Adekastab PEP-8, Adekastab
PEP-8F, Adekastab PEP-8W, Adekastab PEP-11C, Adekastab PEP-24G, Adekastab
PEP-36, Adekastab HP-10, Adekastab 2112, Adekastab 260, Adekastab P,
Adekastab QL, Adekastab 522A, Adekastab 329K, Adekastab 1178, Adekastab
1500, Adekastab C, Adekastab 135A, Adekastab 517, Adekastab 3010,
Adekastab TPP from Asahi Denka K.K.; and the like.
Preferred phosphite antioxidants are the compounds represented by the
formula:
##STR1##
wherein, R.sub.1 represents a hydrogen atom, a t-butyl group, or a phenyl
group, R.sub.2 represents a hydrogen atom, a methyl group, t-butyl group,
or a phenyl group, and R.sub.3 represents a hydrogen atom, or a methyl
group.
Particularly preferred are tris-(4-t-butylphenyl)phosphite having a melting
point of 75.degree. C., tris-(2-t-butyl-4-methylphenyl)phosphite having a
melting point of 110.degree. C., tris-(2-t-butyl-5-methylphenyl)phosphite
having a melting point of 111.degree. C., tris-(2-phenylphenyl)phosphite
having a melting point of 96.degree. C., and
tris-(4-phenylphenyl)phosphite having a melting point of 92.degree. C.
Examples of the thioether antioxidant include those commercially available
as Sumilizer TPL-R, Sumilizer TPM, Sumilizer TPS, Sumilizer TP-D,
Sumilizer TL, Sumilizer MB from Sumitomo Kagaku K.K.; and as Adekastab
AO-23, Adekastab AO-412S, Adekastab AO-503A from Asahi Denka K.K.; and the
like.
Preferred thioether antioxidants are dilauryl 3,3'-thiodipropionate,
ditridecyl 3,3'-thiodipropionate, dimyristyl 3,3'-thiodipropionate,
distearyl 3,3'-thiodipropionate,
bis-(2-methyl-4-{3-n-alkylthiopropionyloxy}-5-t-butylphenyl)sulfide, and
pentaerythritol-tetrakis-(.beta.-lauryl thiopropionate),
2-mercaptobenzimidazol, and the like.
Particularly preferred thioether antioxidants are dilauryl
3,3'-thiodipropionate, ditridecyl 3,3'-thiodipropionate, distearyl
3,3'-thiodipropionate, and
bis-(2-methyl-4-{3-n-alkylthiopropionyloxy}-5-t-butylphenyl)sulfide.
Thus obtained epoxy group-containing acrylic resin (A), polycarboxylic acid
(B), and antioxidant (C) were formulated to obtain the powder coating
composition of the present invention.
The epoxy group-containing acrylic resin (A), and the polycarboxylic acid
(B) are formulated in an amount so that the molar ratio of the epoxy group
contained in the epoxy group-containing acrylic resin (A) to the carboxyl
group contained in the polycarboxylic acid (B) becomes 10/10 to 10/5,
preferably 10/8 to 10/6. If the molar ratio is less than 10/10, the gloss
of the resulting coated film may become poor, and it is more than 10/5,
the curability of the resulting powder coating composition may become
poor.
The antioxidant (C) is contained in an amount of 0.1 to 10 parts,
preferably 0.5 to 8 parts, more preferably 1 to 7 parts by weight, based
on 100 parts of the total weight of the epoxy group-containing acrylic
resin (A) and the polycarboxylic acid (B). If the content of the
antioxidant (C) is less than 0.1 parts by weight, the oxidation inhibiting
ability may become insufficient, and if it is more than 10 parts by
weight, the water resistance and blocking resistance of the resulting
coated film may become poor.
Surface modifier (D)
The powder coating composition of the present invention may optionally
contain a surface modifier (D). The surface modifier (D) is the additive
which promotes fusing of each particles of the powder coating composition,
and improves clearness of the resulting coated film.
A polymer which has good compatibility with particles of the powder coating
composition may be employed as the surface modifier. The polymer employed
is not particularly limited, but those having a SP value of from 10.4 to
11.0, preferably 10.6 to 10.9, and a number average molecular weight of
2500 to 9000, preferably 3000 to 7000, are preferred. The polymer having
such a SP value, generally show good compatibility with epoxy
group-containing acrylic resin, and improves clearness of the resulting
coated film. When the molecular weight of the polymer, which is employed
as the surface modifier, is less than 2500, the blocking resistance of the
resulting powder coating composition becomes poor, and the surface
modifying ability may become insufficient. If the molecular weight is more
than 9000, the smoothness of the resulting coated film may be ruined.
Specific examples of the polymer include acrylic polymers. For example, a
polymer obtained by polymerizing at least one monomers selected from
methyl (meth)acrylate, ethyl (meth) acrylate, butyl (meth) acrylate,
isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, cyclohexyl (meth)acrylate, stearyl (meth)acrylate, and
lauryl (meth)acrylate can be used.
The surface modifier (D) is preferably included in the powder coating
composition of the present invention in an amount of from 0.1 to 4 parts,
preferably 0.3 to 2 parts by weight, based on 100 parts of the total
weight of the epoxy group-containing acrylic resin (A) and the
polycarboxylic acid (B). If the content of the surface modifier (D) is
less than 0.1 parts by weight, the smoothness of the resulting coated film
may be ruined. If it is more than 4 parts by weight, the blocking
resistance of the resulting coated film may become poor.
The powder coating composition of the present invention may further
comprise UV absorbers, hindered amine lightstabilizers, and antioxidants
in order to improve weather resistance of the coated film. The powder
coating composition may also contain additives for modifying flowability
or blocking resistance of the coating composition, or appearance or
blocking resistance of the coated film, such as silicone compounds,
Aerosil, and resin particles.
When using resin particles as an blocking inhibitor, a powder of the resin
particles is generally added and mixed into the powder coating composition
which is prepared beforehand. The resin particles have a mean particle
size of from 0.01 to 10 .mu.m, preferably from 0.03 to 3 .mu.m, a glass
transition temperature of from 50.degree. to 150.degree. C., preferably
from 70.degree. to 120.degree. C., and an SP value of from 9 to 15,
preferably from 10 to 13.
The resin particles having a mean particle size of less than 0.01 .mu.m is
difficult to prepare. If the mean particle size of the resin particles is
more than 10 .mu.m, the addition amount of the resin particles becomes
large because blocking inhibiting ability becomes poor, and appearance of
the coated film may become poor. If the glass transition temperature is
less than 50.degree. C., blocking inhibiting ability becomes poor, and is
more than 150.degree. C., it cannot be used practically. If the SP value
is out of the above range, compatibility with the powder coating
composition becomes poor, and appearance of the coated film may be
damaged.
An addition amount of the resin particles is not particularly limited, but
generally is 0.05 to 20 parts, preferably 0.1 to 10 parts by weight, based
on 100 parts by weight of the powder coating composition. If the addition
amount of the resin particles is more than 20 parts by weight, the
appearance of the resulting coated film may become poor, and if it is less
than 0.05 parts by weight, the blocking inhibiting ability may become
poor.
The powder coating composition of the present invention preferably does not
contain blocked isocyanate as a curing agent. If blocked isocyanate is
employed, the resulting cured coated film may readily become yellow.
Furthermore, the blocking agent which blocks an isocyanate group,
vaporizes when the coating composition is baked. As a result, pinholes may
be generated on the resulting cured coated film.
The powder coating composition of the present invention may be coated on a
substrate by a static coating method and the like. The substrate may be
optionally undercoated or intercoated. Any known coating composition for
that use can be employed as the coating composition for undercoating or
intercoating the substrate.
The powder coating composition of the present invention can be
advantageously used for the substrate such as wood, metal, glass, fabric,
plastic, foam, etc., particularly plastic and surface of metal such as
steel, aluminum and alloys thereof. Generally, thickness of the coated
film varies depending on the desired application. A film thickness of 20
to at 120 .mu.m, preferably 40 to 100 .mu.m, is useful in almost all
cases.
After applying the coating composition on the substrate, the resulting
coating is cured. A uniform cured coated film is formed by baking at
100.degree. to 250.degree. C., preferably 120.degree. to 200.degree. C.
The curing time varies depending on the curing temperature used, but is
usually for 15 to 45 minutes at 120.degree. to 200.degree. C.
In one preferred embodiment of the present invention, a coated film is
provided according to the process which comprises the steps of:
applying an aqueous or solvent-based coating composition on an undercoated
or intercoated substrate to form a base coating;
applying the clear powder coating composition of the present invention
thereon to form a clear powder coating, without curing the base coating;
and
heating and curing both the base coating and the clear powder coating.
The base coating composition employed in the method is not particularly
limited, but is preferably the aqueous coating composition which
comprises:
(a) 95 to 10% by weight (solid) of a film forming vinyl polymer obtained by
at least partially neutralizing an acidic group of a copolymer having a
number average molecular weight of 6000 to 50,000, prepared by
copolymerizing 5 to 40% by weight of an amide group-containing monomer, 3
to 15% by weight of an acidic group-containing monomer, and remainder
amount of the other monomers; and
(b) 5 to 90% by weight (solid) of a urethane-containing aqueous dispersion
obtained by dispersing a hydrophilic group-containing oligomer into an
aqueous medium which contains primary polyamine, secondary polyamine, or
both of them; the hydrophilic group-containing oligomer being prepared by
reacting, in a condition rich in isocyanate, a diol having a terminal
hydroxyl group having a molecular weight of 100 to 5000, a diisocyanate,
and a compound having both at least one active hydrogen and a hydrophilic
group.
EXAMPLES
The following Synthetic Examples, Examples and Comparative Examples further
illustrate the present invention in detail but are not to be construed to
limit the scope thereof. In the Synthesis Examples, Examples and
Comparative Examples, "parts" are by weight unless otherwise stated.
The methods for measuring the characteristic value of the powder coating
composition of the present invention is described below.
Molecular Weight
A polymer solution of the sample was analyzed by using gel permeation
chromatography (GPC) and the number average molecular weight was
calculated based on the molecular weight of polystyrene.
SP Value
The SP value was measured according to the turbid point titration method
described in Sub & Clarke, J. Polymn. Sci., A-1, 5, pages 1671-1681, 1967,
using a tetrahydrofuran (THF) solvent at a measuring temperature of
20.degree. C.
Glass Transition Temperature
The glass transition temperature was measured according to differential
scanning calorimetry (DSC).
Particle Size of the Ground Coating Composition
The weight average particle size was measured by using Microtrack "MK-2"
(manufactured by Nikkiso K.K.) and integrated the value by 50% and
averaged.
Particle Size of the Resin Particles
The weight average particle size was measured according to laser light
scattering method (Coulter Model N4) by using an emulsion of the resin
particles.
Synthetic Example 1
Synthesis of epoxy group-containing acrylic resin (acrylic polyepoxide) (A)
Into a reaction vessel equipped with a thermometer, a stirrer, a cooling
tube, a nitrogen introducing tube and a dropping funnel, 63 parts of
xylene was charged and heated to 130.degree. C. To the vessel, a monomer
mixture consisting of 45 parts of glycidyl methacrylate, 20 parts of
stylene, 27 parts of methyl methacrylate, and 8 parts of isobutyl
methacrylate; and an initiator solution consisting of 6.5 parts of
t-butylperoxy-2-ethyl hexanoate, and 6 parts of xylene are dropwise added
respectively over 3 hours.
After that, the reaction vessel was left at the temperature for 30 minutes,
and an initiator solution consisting of 0.1 parts of t-butylperoxy-2-ethyl
hexanoate and 7 parts of xylene was added dropwise over 30 minutes. After
an end of the addition, the reaction vessel was further left at
130.degree. C. for 1 hour. Xylene was then removed by distillation under
reduced pressure, and acrylic resin A-1 which has a SP value of 11.3, and
a Tg of 52.degree. C. was obtained.
Synthetic Examples 2 to 6
Acrylic polyepoxides A-2 to A-6 were prepared according to substantially
the same manner as described in Synthetic Example 1, except that the
compositions tabulated in the following Table 1 were used.
TABLE 1
______________________________________
Acrylic
polyepoxide (A)
A-1 A-2 A-3 A-4 A-5 A-6
______________________________________
Monomer (a)
GMA 45 40 60 40 45 45
.alpha.-MGM
-- 5 -- -- -- --
Monomer (b)
ST 20 20 23.5 13.2 21.2 1.5
MMA 27 27 8.5 33 28.4 13
iBMA 8 8 8 8 -- 8
nBMA -- -- -- 5.8 5.4 32.5
SP value 11.3 11.5 11.3 11.3 11.3 11.2
Tg (.degree.C.) 52 53 43 50 51 30
______________________________________
GMA: glycidyl methacrylate
MGM: methyl glycidyl methacrylate
ST: styrene
MMA: methyl methacrylate
iBMA: isobutyl methacrylate
nBMA: nbutyl methacrylate
Synthetic Example 7
Synthesis of surface modifier (D)
Into a reaction vessel equipped with a thermometer, a stirrer, a cooling
tube, a nitrogen introducing tube and a dropping funnel, 90 parts of
xylene was charged and heated to 120.degree. C. To the vessel, a monomer
mixture consisting of 50 parts of ethyl acrylate, 50 parts of n-butyl
acrylate, and 3 parts of t-butylperoxy-2-ethyl hexanoate are dropwise
added over 3 hours.
After that, the reaction vessel was left at the temperature for 30 minutes,
and an initiator solution consisting of 0.3 parts of t-butylperoxy-2-ethyl
hexanoate and 10 parts of xylene was added dropwise over 30 minutes. After
the end of the addition, the reaction vessel was further left at
120.degree. C. for 2 hour. Xylene was then removed by distillation under
reduced pressure, and surface modifier D-1 which has a SP value of 10.7,
and a number average molecular weight of 6000 was obtained.
Synthetic Examples 8 to 10
Surface modifiers D-2 to D-4 were prepared according to substantially the
same manner as described in Synthetic Example 7, except that the
compositions tabulated in the following Table 2 were used.
TABLE 2
______________________________________
Surface modifier (D)
D-1 D-2 D-3 D-4
______________________________________
Ethyl acrylate
50 50 50 70
n-Butyl acrylate
50 50 50 30
t-Butylperoxy-
3 6 2.6 3
2-Ethyl hexanoate
SP value 10.7 10.7 10.7 10.9
Mn 6000 3000 7000 6000
______________________________________
Synthetic Example 11
Preparation of resin particles
Into a reaction vessel equipped with a stirrer, a cooler, and a heater, 380
parts of deionized water, and 2 parts of nonionic surfactant "MON 2"
(manufactured by Sanyo Kasei K.K.) were charged, heated to 80.degree. C.
and stirred until the solution becomes homogeneous. A polymerization
initiator solution consisting of 1 part of ammonium persulfate, and 10
parts of deionized water, was then added to the solution.
A solution consisting of 61 parts of methyl methacrylate, 36 parts of
stylene, and 3 parts of butyl methacrylate was added dropwise to the
reaction vessel over 60 minutes. After an end of the addition, the
reaction mixture was stirred at 80.degree. C. for 60 minutes, and the
emulsion having a nonvolatile content of 20%, and a particle size of 0.03
to 0.05 .mu.m. The emulsion was dried by spraying to obtain the resin
particles having a SP value of 10, a glass transition temperature of
110.degree. C., a mean particle size of 0.03 to 0.05 .mu.m.
Example 1
Preparation of powder resin composition
100 Parts of acrylic polyepoxide A-1, 27.3 parts of decanedicarboxylic
acid, 1.27 parts of 2,6-di-t-butyl-4-methylphenol, 2.54 parts of
tris-(4-t-butylphenyl) phosphite, and 0.76 parts of surface modifier D-1
were mixed. The resulting mixture was melted and kneaded by using
"Co-kneader PR-46" (manufactured by Bus in Swizerland), extruded, and
cooled to obtain a solid coating composition.
The composition was grounded ultra centrifugally by using "Ultra
centrifugal grinder" manufactured by Mitamura Riken K.K., and classified
(150 mesh). 0.2 Parts of "Aerosil R-974" manufactured by Nippon Aerosil
K.K. was added to 100 parts of the resulting powder, and well mixed to
obtain powder coating composition I having a mean particle size of 25
.mu.m.
Color difference and blocking resistance of the resulting powder coating
composition were evaluated according to the following procedure. The
results are shown in Tables 3 and 4.
Color Difference
The powder coating composition was directly coated on a white panel such
that the coating thickness has a gradient, followed by baking at
150.degree. C. for 25 minutes to prepare a coated white panel. The b
values of the coated white panel in which the thickness of the clear
coated film is 60 .mu.m, were measured by using the SM color computer
"SM-4" manufactured by Suga Sikenki K.K. The difference of the measured b
values from those of the uncoated white panel was obtained as color
difference (.DELTA.b).
Blocking Resistance
The powder coating composition was filled in a 50 ml jar, and left at
30.degree. C. for 2 months. After that, the content was took out and
inspected whether agglomerates are present or not. Evaluation was carried
out according to the following criteria.
.circleincircle.: No mass was found, the powder showed excellent flow;
.smallcircle.: Certain re-pulverizable masses were found;
x: Many unpulverizable masses were found.
Example 2, and Comparative Examples 1 and 11
Powder coating compositions II, XII, and XVII were prepared according to
substantially the same manner as described in Example 1, except that the
compositions tabulated in the following Table 3 and 4 were used. The mean
particle sizes of the resulting powder coating compositions were shown in
Tables 3 and 4.
Examples 3 to 10, and Comparative Examples 2 to 4
Powder coating compositions III to X, and XIII to XV were prepared
according to substantially the same manner as described in Example 1,
except that the compositions tabulated in the following Table 3 and 4 were
used, and the solid coating composition was jet-ground by using "Labo Jet
LJ-N" manufactured by Nippon Pneumatic K.K. The mean particle sizes of the
resulting powder coating compositions were shown in Tables 3 and 4.
Example 11
2 Parts of the resin particles obtained in Synthetic Example 11 were added
to 100 parts of powder coating composition IV obtained in Example 4, and
the resulting composition was dry mixed by using "Henshel mixer"
(manufactured by Mitsui-miike Seisakusho). Powder coating composition XI
which has resin particles stuck on the surface of the coating particles of
the coating composition, was obtained.
Comparative Example 5
2 Parts of the resin particles obtained in Synthetic Example 11 were added
to 100 parts of powder coating composition XV obtained in Comparative
Example 4, and the resulting composition was dry mixed by using "Henshel
mixer". Powder coating composition XVI which has resin particles stuck on
the surface of the coating particles of the coating composition, was
obtained.
TABLE 3
__________________________________________________________________________
Examples 1 2 3 4 5 6 7 8 9 10 11
__________________________________________________________________________
Composition No.
I II III IV V VI VII VIII
IX X XI
Acrylic polyepoxide (A)
A-1 A-2 A-3 A-4 A-5 A-5 A-6 A-1 A-1 A-1 A-4
100 100 100 100 100 100 100 100 100 100 100
Decanedicarboxylic acid
27.3
24.3
36.4
24.3
24.3
27.3
27.3
27.3
27.3
27.3
24.3
Phenol antioxidant
AO-1
AO-2
AO-3
AO-4
AO-4
AO-4
AO-5
AO-5
AO-5
-- AO-4
1.27
1.24
1.36
1.24
1.24
1.27
1.27
1.27
1.27
-- 1.24
Phosphite antioxidant
AO-6
AO-7
AO-8
AO-8
AO-9
AO-10
AO-6
AO-8
-- AO-8
AO-8
2.54
2.48
2.72
2.48
2.48
2.54
2.54
2.54
-- 2.54
2.48
Surface modifier (D)
D-1 D-1 D-1 D-1 D-1 D-1 D-1 D-2 D-3 D-4 D-1
0.76
0.75
0.82
0.75
0.75
0.76
0.76
0.76
0.76
0.76
0.75
Polysiloxane
0.16
0.15
0.17
0.15
0.15
0.16
0.16
0.16
0.16
0.16
0.15
Benzoin 0.64
0.62
0.68
0.62
0.62
0.64
0.64
0.64
0.64
0.64
0.62
Resin particles
-- -- -- -- -- -- -- -- -- -- 2*
Particle size (.mu.m)
25 24 11 11 11 10 12 10 10 10 11
Color difference (.DELTA. b)
0.22
0.18
0.16
0.15
0.18
0.18
0.17
0.15
0.30
0.25
0.15
Blocking resistance
.largecircle.
.largecircle.
.largecircle.
.largecircle.
.largecircle.
.largecircle.
.largecircle.
.largecircle.
.largecircle.
.largecircle.
.circleincircle.
__________________________________________________________________________
AO-1: 2,6di-t-butyl-4-methylphenol (m.p. 71.degree. C.);
AO2: noctadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate (m.p.
50.degree. C.);
AO3: tetrakis{methylene3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate}
methane (m.p. 115.degree. C.);
AO4: 3,9bis-›2{3(3-t-butyl-4-hydroxy-5-methylphenyl)
propionyloxy1,1-dimethylethyl2,4,8,10-tetraoxaspiro{5,5}undecane (m.p.
125.degree. C.);
AO5: 1›2{3(3,5-di-t-butyl-4-hydroxyphenyl)
propionyloxy}ethyl4-{3(3,5-di-t-butyl-4-hydroxyphenyl)
propionyloxy}2,2,6,6-tetramethylpiperidine (m.p. 135.degree. C.);
AO6: tris(4-t-butylphenyl) phosphite (m.p. 75.degree. C.);
AO7: tris(4-phenylphenyl) phosphite (m.p. 92.degree. C.);
AO8: tris(2-phenylphenyl) phosphite (m.p. 96.degree. C.);
AO9: tris(2-t-butyl-4-methylphenyl) phosphite (m.p. 110.degree. C.);
AO10: tris(2-t-butyl-5-methylphenyl) phosphite (m.p. 111.degree. C.).
*The amount is based on 100 parts by weight of the powder resin
composition.
TABLE 4
______________________________________
Comp. Examples
1 2 3 4 5 11
______________________________________
Composition No.
XII XIII XIV XV XVI XVII
Acrylic polyepoxide
A-5 A-1 A-1 A-6 A-6 A-5
(A) 100 100 100 100 100 100
Decanedicarboxylic
27.3 27.3 27.3 27.3 27.3 27.3
acid
Phenol antioxidant
-- -- -- AO-4 AO-4 AO-1
-- -- -- 1.27 1.27 1.27
Phosphite -- AO-11 AO-12 AO-13 AO-13 AO-6
antioxidant
-- 2.54 2.54 2.54 2.54 2.54
Surface modifier
D-1 D-4 D-1 D-1 D-1 D-1
(D) 0.76 0.76 0.76 0.76 0.76 0.76
Polysiloxane
0.16 0.16 0.16 0.16 0.16 0.16
Benzoin 0.64 0.64 0.64 0.64 0.64 0.64
Resin particles
-- -- -- -- 2* --
Blocked isocyanate
-- -- -- -- -- 6.15
Particle size (.mu.m)
24 10 11 11 11 25
Color difference
1.01 0.35 0.28 0.18 0.18 0.38
(.DELTA.b)
Blocking resistance
.largecircle.
.times. .largecircle.
.largecircle.
.circleincircle.
.largecircle.
______________________________________
Example 12
Preparation of coated plate
A cationic electrodeposition coating composition (Powertop U-50,
manufactured by Nippon Paint Co., Ltd.) and an intermediate coating
composition (Orga P-2, manufactured by Nippon Paint Co., Ltd.) were coated
on a phosphated steel plate having a thickness of 0.8 mm, so that a dry
thickness thereof became 25 and 40 .mu.m, respectively. An aqueous base
coating composition (Example 1 of U.S. Pat. No. 5,183,504, manufactured by
Nippon Paint Co., Ltd.) was air-sprayed on it so that a dry thickness
became about 15 .mu.m, followed by setting at 80.degree. C. for 5 minutes
to form a basecoated film.
Meanwhile, a formulation of the aqueous base coating composition is 56.2
parts of the acrylic resin varnish having a number-average molecular
weight of 12000, a hydroxyl value of 70 mgKOH/g solid, an acid value of 58
mgKOH/g solid and a nonvolatile content of 50% obtained in Preparation
Example 1 of the same reference, 15.0 parts of methyled melamine "Cymel
303" (manufactured by Mitsui Cytec Co., Ltd.), 21.5 parts of an urethane
emulsion having an acid value of 16.2 mgKOH/g solid and a nonvolatile
content of 33%, 7.5 parts of an aluminum pigment paste "Alpaste 7160N"
having an aluminum flake content of 65% (manufactured by Toyo Aluminum
Co., Ltd.) and 1.0 part of isostearic acid phosphate "Phosphorex A-180L"
(manufactured by Sakai Kagaku Co., Ltd.).
Powder coating composition I obtained in Example 1 was coated static
electrically by wet on wet method so that thickness of the powder clear
coating became about 60 .mu.m, followed by baking at 150.degree. C. for 25
minutes to form a coated plate.
The performance of the resulting coated films was tested as follows. The
results are shown in Table 5.
Appearance
A surface of the coated film was observed visually, and smoothness and
gloss thereof were evaluated according to the following criteria.
.smallcircle.: good x: bad
Water Resistance
The coated film was dipped in tap water of 40.degree. C. for 10 days, and
thereafter, a surface of the coated film was observed visually and
evaluated according to the following criteria.
.smallcircle.: No change is recognized.
x: Change is recognized.
Xylol Resistance
A surface of the coated film was rubbed back and forth 10 times by using a
piece of gauze saturated with xylene, and thereafter, the surface of the
coated film was observed visually and evaluated according to the following
criteria.
.smallcircle.: No change is recognized.
x: Traces are recognized.
Example 13
Preparation of coated plate
A cationic electrodeposition coating composition (Powertop U-50,
manufactured by Nippon Paint Co., Ltd.) and an intermediate coating
composition (Orga P-2, manufactured by Nippon Paint Co., Ltd.) were coated
on a phosphated steel plate having a thickness of 0.8 mm, so that a dry
thickness thereof became 25 and 40 .mu.m, respectively. A solvent type
high-solid base coating composition (manufactured by Nippon Paint Co.,
Ltd.) was air-sprayed on it so that a dry thickness became about 16 .mu.m,
followed by setting for 7 minutes to form a basecoated film.
Meanwhile, a formulation of the solvent type high-solid base coating
composition is 20 parts of an acrylic resin (nonvolatile content 80%,
hydroxyl value 100 mgKOH/g solid, acid value 30 mgKOH/g solid,
number-average molecular weight 1800) manufactured by Nippon Paint Co.,
Ltd., 30 parts of a polyester (nonvolatile content 80%, hydroxyl value 100
mgKOH/g solid, acid value 12 mgKOH/g solid, number-average molecular
weight 2600) manufactured by Nippon Paint Co., Ltd., 40 parts of a
melamine resin "Cymel 202" (nonvolatile content 80%) manufactured by
Mitsui Cytec Co., Ltd., 10 parts of a melamine resin "Cymel 327"
(nonvolatile content 90%) manufactured by Mitsui Cytec Co., Ltd., "Alpaste
Al 60-600" (nonvolatile content 65%) manufactured by Toyo Aluminum Co.,
Ltd. and 7 parts of isopropyl alcohol.
Powder coating composition I obtained in Example 1 was coated static
electrically by a wet on wet method so that thickness of the powder clear
coating became about 60 .mu.m, followed by baking at 150.degree. C. for 25
minutes to form a coated plate.
The performances of the resulting coated films were tested according to
substantially the same manner as described in Example 12. The results are
shown in Table 5.
Examples 14 to 23 and Comparative Examples 5 to 8
The coated plates are prepared in substantially the same manner as that
described in Example 12, except that the coating compositions tabulated in
the following Table 5 were used. The performance of the resulting coated
films was tested in substantially the same manner as described in Example
12. The results are shown in Table 5.
TABLE 5
______________________________________
Coating composition Appear- Water Xylol
Examples
base top (powder)
ance resist. resist.
______________________________________
12 aqueous I .largecircle.
.largecircle.
.largecircle.
13 solvent I .largecircle.
.largecircle.
.largecircle.
14 aqueous II .largecircle.
.largecircle.
.largecircle.
15 aqueous III .largecircle.
.largecircle.
.largecircle.
16 aqueous IV .largecircle.
.largecircle.
.largecircle.
17 aqueous V .largecircle.
.largecircle.
.largecircle.
18 aqueous VI .largecircle.
.largecircle.
.largecircle.
19 aqueous VII .largecircle.
.largecircle.
.largecircle.
20 aqueous VIII .largecircle.
.largecircle.
.largecircle.
21 aqueous IX .largecircle.
.largecircle.
.largecircle.
22 aqueous X .largecircle.
.largecircle.
.largecircle.
23 aqueous XI .largecircle.
.largecircle.
.largecircle.
Comp. 6 aqueous XII .largecircle.
.largecircle.
.largecircle.
Comp. 7 aqueous XIII .circleincircle.
.largecircle.
.largecircle.
Comp. 8 aqueous XIV .times.
.largecircle.
.largecircle.
Comp. 9 aqueous XV .largecircle.
.times. .largecircle.
Comp. 10
aqueous XVI .largecircle.
.times. .largecircle.
Comp. 12
aqueous XVII .times.
.largecircle.
.largecircle.
______________________________________
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